1. Field of the Invention
The present invention relates to a communication system, a communication terminal, and a method for performing communications among a plurality of communication terminals.
2. Description of the Related Art
In a wireless communication system, an infrastructure mode and an ad hoc mode are used. In the infrastructure mode, a plurality of wireless communication terminals communicates with one another via a base station or an access point (hereinafter simply referred to as an “AP”), while in the ad hoc mode, a plurality of wireless communication terminals directly communicates with one another by bypassing the AP.
In a network created by using the ad hoc mode (hereinafter simply referred to as an “ad hoc network”), a signal including information necessary for the wireless communication, which is referred to as a “beacon”, is notified to a peripheral wireless communication terminal. The “beacon” signal is transmitted to and received by each terminal at random. Thus, the wireless communication terminals can operate in synchronization with one another and data communication among the terminals is performed.
Conventional processing for performing a wireless connection in the ad hoc network includes processing for transmitting (broadcast-transmitting) a search signal called “probe request” to all terminals on the network and processing for receiving a response called “probe response”. More specifically, the following processing is conventionally performed in performing a data communication among a plurality of wireless communication terminals.
If a wireless communication terminal has not received a “probe response”, although the wireless communication terminal has transmitted a “probe request” for a predetermined number of times, then the wireless communication terminal starts transmitting the signal “beacon”.
More specifically, in this case, the wireless communication terminal itself creates an ad hoc network and starts transmitting a notification signal to peripheral wireless communication terminals. Then, if the wireless communication terminal has received a “probe request”, the communication among the wireless communication terminals starts. Thus, the data communication in the ad hoc network created in the above-described manner is implemented.
On the other hand, in the case where the wireless communication terminal has received a “probe response” after a “probe request” has been transmitted, the wireless communication terminal that has transmitted the “probe request” acquires synchronization information or transmission rate information about the network according to the received response signal.
Then, communications among the wireless communication terminals are started and the wireless communication terminal joins the existing ad hoc network. Thus, the data communications with the peripheral wireless communication terminals are implemented (in compliance with Institute of Electrical and Electronic Engineers (IEEE) STD 802.11-1999 Part 11: Wireless Local Area Network (LAN) Medium Access Control (MAC) and Physical Layer (PHY) Specifications).
Here, a case is described where a wireless communication terminal joins an ad hoc network created by and including a plurality of other wireless communication terminals that complies with a communication standard (hereinafter simply referred to as a “communication method” where necessary) different from the communication method that the wireless communication terminal joining the ad hoc network complies with.
For example, suppose that a plurality of wireless communication terminals, which complies with the IEEE802.11n standard, has created an ad hoc network, and that a data communication among the wireless communication terminals at a unique high transmission rate defined by the IEEE802.11n standard has been performed. Then, a wireless communication terminal A, which complies with only the IEEE802.11b standard, has issued a request for joining the ad hoc network.
In this case, at first, the wireless communication terminal A transmits a “probe request”. Then, the wireless communication terminal A receives a response to the “probe request”, namely, a “probe response”.
In the transmission rate information included in the “probe response”, a transmission rate that the wireless communication terminal A does not comply with is defined.
This state indicates that the wireless communication terminal A has issued a request for joining the ad hoc network created by and including a plurality of wireless communication terminals that complies with a communication method different from the communication method that the wireless communication terminal A complies with. Accordingly, in this case, because the wireless communication terminal A does not have a capacity to perform the data communication at the high transmission rate defined by the communication method used by the wireless communication terminals, the wireless communication terminal A cannot join the ad hoc network.